It is known that the spark does not jump precisely at the end of compression, when the piston reaches top dead centre, and that a certain advance is necessary, or on occasions a lag of the ignition with respect to the said top dead centre, due to the fact that the explosion of the mixture is not instantaneously propagated in the chamber or cylinder.
Logically the greater the speed of the engine, the greater should be the advance angle of the ignition. This is shown by way of example in a centrifugal advance curve in FIG. 8.
In the same manner, it is also known that the firing is propagated at a higher speed if the mixture is highly compressed, that is to say, if the filling of the cylinder is completed, due to the fact that the throttle is fully open. A lesser degree of advance would be required wih the throttle in an intermediate position giving a less rich mixture. This also is shown by way of example in FIG. 10.
Therefore it is a question of attaining the optimum degree of advance in relation to the foregoing variables, limiting this to the centrifugal and manifold vacuum advance, and position of the throttle butterfly, consequently rendering the device fully automatic.
The following description of the disclosed invention is given by way of example.
It is assumed that the crankshaft speed (and thus the piston position) is given by the output of a distributor pick-up (or better by a crankshaft pick-up) which provides an electrical signal in the form of a square wave having a fixed duty cyle. This should ideally be of the optical type but can be of a type using variations in magnetic flux or of other known types.
The signal given by the pick-up or transducer follows: EQU d = r/T
where d is the duty cycle, r is the pulse width and T is the period between pulses. It will provide two or more pulses for each crankshaft revolution, in the case of four cycles engine having four or more cylinders (four or more pulses for each distributor revolution). In FIG. 9 an ideal electrical output signal from a transducer as the heretofore described in shown, also the output signal of the invention described is shown as being generated under ideal conditions (constant velocity, normal ambient temperature, etc.).